The six studies proposed here focus on changes in semantic structure that may accompany aging. The objectives are: (a) to develop methods for the investigation of age related changes in lexical structure and word encoding, and (b) to specify changes in lexical structure and word encoding that occur during maturity, particularly in old age. Since the cognitive changes that accompany aging show considerable variation among individuals, emphasis is placed on methods which enable the specification of individual differences. Two aspects of semantic structure will be examined. First, adult age differences in the way in which words are encoded in short-term memory will be investigated by examining the patterns of interference generated in a discrete trial Stroop color-naming task. Second, adult age differences in the structure of word meanings in the mental lexicon will be studied using an individual differences multidemensional scaling procedure (INDSCAL).